Field of the Invention
This invention relates to rotary drive apparatus and, more particularly, to rotary drive apparatus in which a single driven element is connected by a cable to a plurality of driving elements, each of which is connected to a motor for imparting rotary motion to the driven element to rotation of the driven elements.
Description of the Prior Art
U.S. Pat. No. 4,351,197 (Carson) discloses several embodiments of rotary drive apparatus in which a threaded screw is connected by cable to a single driven element, namely a drum. A motor causes the driving element to rotate, and the cable connection between the driving element and the driven element imparts rotary movement to the driven element or drum. A single drive shaft is used as the driving element.
A primary advantage of utilizing more than one drive shaft is redundancy for applications requiring high rotatability and low probability of failure. If several drive shafts are used, and one should fail, the remaining shafts will continue to operate.
For applications requiring extremely high torques, the drive apparatus may require more torque than can be obtained with a single drive element. For example, using a single electric motor limits the torque to the output of the single motor. If either the motor size or torque is a limitation, several motors may simultaneously drive a single drum by the apparatus of the present invention.
In applications where extreme rotational drive smoothness is critical, the use of multiple drive motors may be advantageous because the motors may be rotationally positioned relative to one another so that the magnetic cogging imparted by the motors is minimized.
The use of multiple shafts may have other advantages also. For example, one or more of the drive shafts may be utilized as a driven shaft which may be used to drive a shaft angle encoder, tachometer, or other device.
A further advantage of using multiple shafts is in increasing the rotary stiffness of the system. Stiffness varies with the spacing between rotary members, the number of cables used, and the number of shafts. By increasing the number of shafts, the greater the stiffness of the system.